It is required for cellular telephone operation for a cellular phone to be aware of what cell it is located within. Cells in the cellular telephone system refer to the area covered by singular cellular tower, and can overlap. In general, a cellular phone will monitor the control channel of the cellular tower having the strongest signal. Therefore, a cellular phone has a rudimentary knowledge of its location.
However, there are applications, other than the normal voice communications capabilities of the cellular phone, that may require a more exact knowledge of the phone's location within a cell. These include, for example, an application providing location sensitive advertising over the cell phone, wherein targeted advertising could be sent to cell phone users within a certain proximity of the advertiser's location. Other such applications would be the provision of travel directions based on current location and enhanced 911 emergency services from calls made using a cellular phone.
To improve certain characteristics of GPS receiver performance, such as time-to-first-fix and sensitivity, it is possible to provide to the receiver various aiding information, such as a GPS satellite ephemeris, the approximate time and a reference location. The reference location is an approximation or estimate of the receiver's current position, which, when used with other information, allows the receiver to determine which GPS satellites should be visible and to estimate the signal transit times from the each satellite. Generally, without this aiding information, acquiring the satellite signals and computing the receiver's exact location could take much longer. This delay could have serious impacts on the performance of mobile location-based services, which tend to be time-sensitive.
It is therefore desirable to provide a means by which a reference location and other GPS-related information can be provided to a GPS receiver which is integrated into a cellular phone. It is known in the prior art to provide such information via the cellular network. U.S. Pat. No. 5,365,450 (Schuchman et al.) describes an approach wherein the network transmits GPS satellite ephemeris and other information to a GPS-equipped mobile communication device, which then utilizes this information to acquire the GPS satellite signals and to compute a position estimate. Other methods are described in U.S. Pat. Nos. 5,418,538 (Lau) and 5,883,594 (Lau).
One problem with these approaches is that the GPS-equipped cellular phone may at times be situated within a cell not having access to the GPS-related information. Therefore, it would be desirable to be able to provide this information from another, alternate source. Further, once the capability is established to provide the data from an alternate source, it would be desirable to be able to utilize the alternate source to provide other, application-specific types of data.